1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having an improved structure of a fixing unit to fix a transferred image to a recording medium.
2. Description of the Related Art
An image forming apparatus transfers a digital image signal from a computer or a scanner to a recording medium such as printing paper.
Such an electrophotographic image forming apparatus comprises a photosensitive drum to which an electrostatic latent image is imaged, a developing unit to affix a developer to the photosensitive drum, a transfer roller to transfer the developer affixed to the photosensitive drum to the printing paper, and a fixing unit to fix the transferred developer to the printing paper, thereby printing an image on the printing paper. The electrophotographic image forming apparatus may be a laser beam printer, a light emitting diode (LED) printer, a digital copier, etc.
In the electrophotographic image forming apparatus, the fixing unit comprises a heat roller assembly having a heat roller to fix an image by coming into rolling-contact with the printing paper having the transferred image, and a pressing roller disposed facing the heat roller across the printing paper and pressing the printing paper toward the heat roller.
FIG. 1 is a perspective view of the heat roller assembly of a conventional image forming apparatus. As shown therein, a heat roller assembly 141 comprises a heater (not shown), a heat roller 145 heated by the heater and coming into rolling-contact with printing paper (not shown), a gear cap 151 provided in a first end of the heat roller 145, and an end cap 161 provided in a second end of the heat roller 145.
The heat roller 145 has a cylindrical shape, and is provided with the heater. Further, the heat roller 145 is provided with a coated portion 147, which is coated with a nonconductive material on an outer circumferential surface of the heat roller 145, to be in contact with the printing paper. Further, the first and second ends of the heat roller 145 are formed with female screws 146 to which the gear cap 151 and the end cap 161 are coupled, respectively.
The gear cap 151 comprises an insertion portion 152 formed with a male screw on an outer circumferential surface thereof to be coupled to the first end of the heat roller 145, and a gear portion 155 provided in an outside of the insertion portion 152 and formed with a toothed circumference.
Like the gear cap 151, the end cap 161 comprises an insertion portion 152 formed with a male screw on an outer circumferential surface thereof to be coupled to the second end of the heat roller 145.
Thus, the gear cap 151 and the end cap 161 are coupled to the first and second ends of the heat roller 145, respectively.
But in the heat roller assembly 141 of the fixing unit provided in the conventional image forming apparatus, the gear cap 151 and the end cap 161 are screw-coupled to the first and second ends of the heat roller 145, respectively. Therefore, when the printing paper is jammed between the heat roller 145 and the pressing roller (not shown), the gear cap 151 and the end cap 161 are likely to be loosened or separated from the heat roller 145 by a backlash of the heat roller 145.
Also, the heat roller 145 is manufactured to be thin to increase conductivity of heat dissipated from the heater, so that it is difficult to form the female screws on the opposite ends of the thin heat roller 145. Therefore, it is not easy to couple the gear cap 151 and the end cap 161 to the heat roller 145.